Plastic articles



June H, 1963 H. D. 50665 PLASTIC ARTICLES 2 Sheets-Sheet 1 OriginalFiled Sept. 29, 1954 INVENTOR HERBER T 0. B0 665 ATTORNEYS June M, 19%3H. D. BOGGS 3,09

PLASTIC ARTICLES Original Filed Sept. 29, 1954 2 Sheets-$heet 2 KY6 12.,Ff 130 LAYERS SLEEVING N w 8 0 \l m 0 ILAYERS SLEEVING N u; a m 6) \l mIO [5 go 25 3055 40 45505560 5 10 I5 503540 so 556 POUNDS IN I000 POUNDSIN IOO .OO4MESH BETWEEN THREADS 60HELIX .O037NSH BETWEEN THREADS 60HELIXLAYERS SLEEVING -u m-l w -muu6i\lmc0 5 l0 I5 20 25 so 4o 45 so 55 6o 5I0 15 20 253035 404550556065 POUNDS IN |00# POUNDS IN IOO# .0272MESHBETWEEN THREADS HELIX .OOIMESH BETWEEN THREADS HELIX 1 N VENTORHERBERTD. B0665 ATTORNEYS 3,093,160 PLASTIC ARTICLES Herbert D. Boggs,Tulsa, 01th., assignor, by mesne assignments, to H. D. Boggs Company,Ltd, flmaha, Nebn, a limited partnership Continuation of abandonedapplication Ser. No. 459,092, Sept. 29, 1954. This application Dec. 4,1959, Ser. No.

2 Claims. (Cl. 1ss 140 This invention relates to fibrously reinforcedelongated plastic articles including hollow elongated pressure conduits,such as piping.

The production of fibrously reinforced plastic piping is currentlyundergoing a great expansion, with the rate of production increasing asnew applications for such plastic pipings are found. It has becomeincreasingly apparent that the only limiting factor on the expansion ofthe industry is in the capacity of such piping to withstand large andsustained hydraulic, or other, pressures. As the thermosetting resinousmaterials usually used in the fabrication of plastic piping haverelatively low shearing and tension failure coefiicients, any increasesin the pressural capacities of such piping must be derived from thestrengthening of the cage formed by the fibrous reinforcement materialand of the bond between the plastic and this material.

It has previously been proposed to form the fibrous reinforcement from amat of glass fibers which is wrapped about a mandrel, or other object,to form a cylindrical tube. It has been further proposed to form such atube by helical-1y winding a strip of such matting material about amandrel. These mats have been formed of randomly oriented fibers, or, onsome occasions, have been formed of fibers which are p re-oriented toparticular directions to give special shrinkage and setting reactions.

The use of inorganic fibrous reinforcement materials, such as glass, hascreated an entirely new technolog as frequently the difference betweensuccess and failure depends upon the recognition of several finetolerances and the understanding of the correct use of many variablecharacteristics of the materials being utilized. From a strengthviewpoint, it is desirable to have a large ratio, by weight, of glass toplastic, yet obviously, such a formula has practical limits inasmuch asthere must always be sufficient plastic material present to form aproper bond between all the filaments of the reinforcing element. Also,an increase in the proportion of glass will, generally speaking, tend toincrease the overall strength of the cage and will thereby act toincrease the burst strength of the finished pipe. As a matter ofpractical experience, it has been determined that the maximum glass toplastic ratio is between 45% and 60% by weight.

The amount of space between the individual reinforcement fibers affectsthe volume of the mass of the resinous material in a pipe of givengeneral dimensions, and therefore directly affects the total amount ofthe casting shrinkage. It has been considered important that the totalamount of the shrinkage be held to rather small limits as the shrinkageof such resinous material results in a stress being induced in themechanical bond between the resinous material and individual fibers ofthe reinforcing element. This shrinkage is bound up in dozens of tinyvolumes of resin between the filaments or fibers of the reinforcementand is transmitted to the mechanical bond between the plastic and theglass.

Shrinkage occurs when polymerization or therm-osetting takes place. Itreduces the cast resinous body and can be stated in percentage ofreduction of the size of the body. If, through adhesion to the moldcavity, or to the fiber reinforcement, the shrink is retarded in one ormore directions, pent-up stresses are cast into the resinous bodyPatented June 11, 1963 which pre-load the bond to the mold cavity or tothe fiber. Thus, failure in this composite material results from theadditional stress that it takes to break the bond between the resinousmass and the glass fibers. Minute parting at the resin-to-glass fiberline results in pin hole leaks, which can finally result in bursting ofthe pipe when a randomly oriented fibrous reinforcement mat is used.

It, therefore, follows that the spacing between each of the individualfibers of the reinforcement structure should be as small as possible; infact, it is within the contemplated idea that the fibers lay next to oneanother in a contacting or semi-contacting relationship. In an endeavorto place the fibers next to one another, or contacting one another, itis, of course, quite likely that some of the neighboring fibers will bepressed against one another, that is, with a negative clearance. Whilesuch a juxtapositioning is not necessarily undesirable, care must betaken that the fibrous elements are not compressed against one anothertoo tightly. In such a case, the resin will be unable to flow betweenthe elements and it is imperative that there be sufiicient flow to wetand surround every fiber in the reinforcement element. That is to say,if the resin is unable to flow through the spaces between the fibers,dry conditions or spots will exist, and such imperfection-s leaveopenings through which leakage will ultimately occur. It will,therefore, be seen that the optimum spacing between the individualfibers will be controlled inter alia by the viscosity of the particularresinous material being used to form the liquid settable mass.

As it is within the contemplation of this invention to form areinforcement element of interwoven glass fibers which have beengathered into bundles or threads, it will be seen that as the bundlesizes become larger, the area between the bundles becomes greater, thusincreasing the volume of the mass of resinous material which, in turn,increases the total shrink. It is for this reason that the size of thebundles of filaments becomes one of the critical factors in theproduction of fibrously reinforced plastic piping which can sustainlarge and prolonged internal hydraulicstresses. It has also been foundthat greater pipe strengths are directly related to the maximum amountof glass that can be placed in the structure without undue compressionof the fibrous material, causing an improper wetting. I

Fiber arrangement, weave, braid or placement, as will be discussedhereinafter, are also relatedto this bundle and filament size factor. InView of the fact that some of the pin-hole leakage occurs through meshopenings in the fibrous material, particularly where the reinforcementis uniform in pattern, a random placement, that is, an outof-lineplacement of the elements of the various layers of fibrous material willdecrease the great pressure concentration in resin-rich areas and thusincreases the overall capacity of fibrously reinforced plastic piping.Random mat has a broken layering within the mat thickness itself andthus the broken mesh openings are continued as one layer is placed overanother. Cloth convolutely wrapped will, for the most part, result in abroken mash pattern from layer to layer, but this becomes less effectiveas the mesh openings become larger.

A good pattern or form of fibrous reinforcement must have certain otherphysical qualities if an optimum performance is to be attained. Forexample, the reinforcement material selected must have proper de-bulkingcharacteristics, that is the fibrous element must lay fiat and smoothwithin the mold, since folds and wrinkles hinder reinforcement, andweaken the structure to the tensile strength of the resin which, asstated above, is not great. While the burst strength of piping might besaid to be the most important factor, it will be readily seen that pipesare often subjected to external forces and that a low structuralstrength diminishes the scope of utility of a particular pipe section.It is, therefore, highly desirable to provide a fibrous reinforcementpattern which can contribute substantially to the structural strength ofthe composite section formed therewith.

The fibrous reinforcement must also be formed in such a manner that thefilaments, bundles or threads are not easily disturbed or moved fromtheir predetermined locations during its placement within the moldingapparatus, as any such movement will result in resin-rich areas which,as stated above, will often lead to a premature failure of the piping ata point well below its design pressure.

Being aware of all of these problems and variables discussed above, itis therefore an object of this invention to provide an improvedfibrously reinforced plastic pressure conduit having an improved fibrousplacement which gives a uniform high strength.

It is a further object of this invention to provide a fibrouslyreinforced plastic pressure conduit which has a higher strength and alower production cost than such articles made under methods heretoforepracticed.

It is a further object of this invention to provide a fibrouslyreinforced pipe having a reinforcement element which will de-bulkproperly when placed within a casting mold.

It is another object of this invention to produce a pipe which can withuniformity and certainty be designed to meet specific requirements; forinstance, if high hoop strength to resist burst is required, or if highlongitudinal strength is required, the pipe can be made for thesespecific conditions.

It is yet another object of this invention to control the thread sizeand spacing of the reinforcement material in order to get uniform andthorough penetration of the sleeve by the plastic material.

It is still another object of this invention to produce a pipe in whichthe operating conditions of production are not as critical as in theplastic pipes heretofore produced.

It is still another object of this invention to provide fibrouslyreinforced plastic pipe having a reinforcement element which has one ormore layers prefixed or stiffened to provide an arch strength thereforprior to being inserted within a casting mold.

These and other objects of this invention will be apparent from theconsideration of the following description of a specific embodiment,shown for the purpose of illustration, in the accompanying drawings inwhich:

FIGURE 1 is a perspective View of a pressure conduit having a seamlesstubular interwoven fibrous reinforcement element;

FIGURE 2 is a greatly enlarged plan view of a segment of the interwovenseamless reinforcement element;

FIGURE 3 is a greatly enlarged plan view of a modified segment of aninterwoven seamless reinforcement element;

FIGURE 4 is a greatly enlarged plan view of another modified segment ofan interwaven seamless reinforcement element;

FIGURE 5 is a section taken along line 5-5 of FIG- URE 1;

FIGURE 6 is a greatly enlarged fragmentary view of the sectionillustrated in FIGURE 5;

FIGURE 7 is an exemplary sectional view illustrating the relation ofthread size to the resin area;

FIGURE 8 is an exemplary perspective view illustrating the relationbetween interwoven threads and the mass of resin disposed within themesh opening of the threads;

'FIGURE 9 is an exemplary sectional view illustrating the relation ofthe threads of the superposed reinforcement layers;

FIGURE 10 is another exemplary sectional view illustrating the preferredrelation of the threads of the superposed reinforcement layers;

FIGURE 11 is a graphical representation of the relation between thenumber of layers of sleeving and the pressural capacity, in hundreds ofpounds per square inch, and illustrates the point at which leakage willoccur, when there is a .0272 inch mesh opening between threads, thethreads being oriented in a 60 helix;

FIGURE 12 is a graphical representation of the relation between thenumber of layers of sleeving and the pressural capacity, in hundreds ofpounds per square inch, and illustrates the point at which leakage willoccur, when there is a .004 inch mesh opening between threads, thethreads being oriented in a 60 helix;

FIGURE 13 is a graphical representation of the relation between thenumber of layers of sleeving and the pressural capacity, in hundreds ofpounds per square inch, and illustrates the point at which leakage willoccur, when there is a .0037 inch mesh opening between threads, thethreads being oriented in a 60 helix; and

FIGURE 14 is a graphical representation of the relation between thenumber of layers of sleeving and the pressural capacity, in hundreds ofpounds per square inch, when there is a .001 inch mesh opening betweenthreads, the threads being oriented in a 70 helix.

In FIGURE 1, there is illustrated a seamless plastic pipe 10 having atubular seamless interwoven sleeve embedded therein to form areinforcement element. The pipe may be cast of any of a number ofthermosetting resinous materials, such as polyester resins, epoxy resinsor phenolic-epoxy resins. The interwoven sleeves 11 are made up ofthreads formed from filaments of glass fiber. Such filaments of glassfiber are commonly segregated together into bundles consisting of 204filaments which are sometimes termed an end or a strand. A thread is anend or a bundle of ends which have been twisted, therefore, for thepurpose of this disclosure, the term thread will be applied to anysegregated group of glass filaments, and no distinction will be made,except where indicated, between threads formed of twisted filaments, andthreads formed of filaments lying straight in their natural state.

The interwoven pattern of the thread making up the tubular seamlessreinforcement sleeves is illustrated in FIGURES 2, 3 and 4. The enlargedfragmentary segment illustrated in FIGURE 2 is a braid in which thestitches 12, which are made up of two or more threads, are passed overother stitches 12, made up of two or more threads. It will be seen thatthe threads, and therefore the stitches, are oriented at an angle withthe longitudinal axis of the pipe, which is indicated by the center line18.

In FIGURE 3, there is illustrated an enlarged fragmentary segment of atubular seamless reinforcement sleeve which is formed with interwoventhreads. That is, the threads pass over and under relativelytransversely extending threads 14. It will be seen that the threads areoriented with, or are at right angles with, the longitudinal axis of thetube, here represented by the center line 18. That is to say, some ofthe threads extend longitudinally of the pipe and parallel to this axis,while the other threads extend peripherally of the tube, or at rightangles to its longitudinal axis. In FIGURE 4, there is illustratedanother interwoven pattern in which two threads 16, forming a stitch,extend over and under relatively transversely extending pairs of threads16, which also form stitches. In some applications, this pattern ofweaving is superior to that illustrated in FIGURE 3, inasmuch as lesscrimp is placed upon the individual threads.

For convenience, this application will refer to a reinforcement patternas being braided when the stitches cross two or more relativelytransversely extending stitches and extend obliquely relative to thelongitudinal axis of p the pipe, that is, when they form a helix aboutthe axis of the pipe. All other patterns are hereinafter deemed to bewoven, when the stitches or threads forming the mesh extendlongitudinally of, and peripherally of, the pipe.

While the size of the threads or stitches, and hence of the compositesection formed by braiding or weaving, is a matter of choice, someparticular sizes of threads will form a superior tubular seamless sleevefor a particular size or O.D. pipe. As stated hereinabove, the smallerthe sizes of the particular threads, the less space there will bebetween the various thread elements and thus a higher proportion, byweight, of glass to resin is possible. In FIGURE 7, there is anexemplary showing of the relation between thread size and the volume ofthe mass of plastic material 22 between the threads 20-. In FIG- URE 8,there is illustrated the relation of the interwoven threads 24 and themass of resin 26 disposed within the mesh opening. It will be seen thatwhen the thermosetting shrinkage occurs, the volumetric reduction in themass of the resin places a stress upon the mechanical bond between theresin and the glass. It, th refore, follows that as the size of thethreads and the mesh openings decrease, the total shrink, and hence theshrinkage stress, is reduced.

Glass filaments may be procured in various end sizes and are designated,for example, as 225, 150 or 75, which means that there are 22,500,15,000, or 7,500 yards, respectively, of filament in a pound. As statedabove, an end consists of 204 filaments segregated together. It is,therefore, evident that the end sizes take up their designation from thefilament diameter. That is, for example, a 225 end size is made up of204 filaments, each .00028 inch in diameter; a 150 end size is made of204 filaments, each .00038 inch in diameter; and the 75 end size is madeup of 204 filaments, each having a diameter of .00053 inch.

In one preferred embodiment of this invention, the threads have beenformed from a 150 end size with 12 ends formed with 1 to 2 twists perinch of the thread. However, excellent results have also been obtainedby using 10 ends formed with 4 to 9 twists per inch. Generally speaking,satisfactory results may be obtained with twists per inch varying from 1to 8, with the filament size varying from 75 to 225. It has also beendetermined that an excellent reinforcement pat-tern may be formed usingthreads or strands which have not been twisted. In such a case, thestrands are kept under an even tension when the interwoven pattern isbeing formed.

Referring more particularly to the formation of a seamless tubularreinforcement element with a braided pattern as illustrated in FIGURE 2,the threads 12 are oriented to form a helix angle with the longitudinalaxis 18 of the tubular element. When this helix angle is relativelysmall, the pipe so reinforced will be strengthened to resist exteriorlongitudinal forces, whereas when the helix angle is increased, theresistance to radial forces, that is the hoop or burst strength of thepipe, will be increased. While satisfactory results may be obtained withany of a large number of helix angles, the embodiment illustrated inFIGURE 2 has its threads oriented at a helix angle of 45.

In accordance with this invention, the seamless tubular sleeving isbraided or woven On a mandrel using ends of a desirable filament sizeand with a suitable number of threads joined in the formation of thestitches. If two or more sleeves 11 are used, they are arrangedconcentrically, that is, one on top of or around the other, as bestillustrated in FIGURES and 6. It is preferable to spray the first orinner layer with a fixative material during or after the braiding orweaving so as to give it arch strength to hold up the other layers andalso to facilitate the withdrawal of the mandrel from the sleevingelement after the mandrel has served its purpose. In some cases, it hasbeen found desirable to spray the fixative material on several of theinner layers or, in some cases, on all of the layers.

The successive braided sleeves may be formed with their threads orientedat varying helix angles ranging from 45 to 70. For example, theinnermost sleeve may be formed with a helix angle of 45 while theoutermost sleeve has a helix angle of 70. When multiple layers are used,each successive braided sleeve can have a progressively varying helixangle between that of the innermost and outermost sleeve. This resultcan be achieved by forming each of the successive sleeves or layers in apattern having a different helix angle, with each of the sleeves havinga diiferent diameter. It is within the contemplation of this inventionto form the various layers from threads having varying helix angle ornumbers of t-wists per inch.

It is also within the contemplation of this invention that all of thesleeving be originally uniformly braided to the same sleeve diameter andthen laid up, layer upon layer, upon the mandrel. When this is done, theinner layer will have the smallest helix angle because the drawing ofthe next layer over the first tends to increase the diameter of thesecond layer and thus distorts its weave in a manner which increases itshelix angle. This result is very advantageous, as then theinterstitches, if any, in the adjacent layers will not line up and thusthe tendency of the resin to flow through too freely will be retarded.There will be a broken or heterogenous mesh pattern radially of the pipeand, therefore, there will be fewer, and smaller, resin-rich areas. Asshown in FIGURE 9, if the threads 28 of the various layers are arrangedin radial alignment, there will be a straight shear line 30 extendingradially of the pipe. in FIGURE 10, there are illustrated threads 32 ofthe superposed layers arranged in a broken or heterogenous mesh patternhaving a longer, stronger line of resistance. It will be seen that thearrangement illustrated in FIGURE 10 results in a smaller resin areawhich contributes to a reduction in shrinkage stress.

As the interwoven seamless tubular reinforcement elements have a certainstiffness, which may be increased by the addition or spraying of afixative as discussed hereinabove, they will de-bulk properly whenplaced in the mold. That is, the elements will not wrinkle or foldcreating bunches, folds, and resin-rich areas. The resinrich areacondition in a pipe results in certain stresses being taken up by theresin, and, hence, transferred to the resin-fiber b ond. It is, ofcourse, desirable that some of the stress be taken up by the cage formedby the glass fibers themselves, rather than by the mechanical bondbetween the resin and the fibers.

After an appropriate number of layers of sleeving have been braided onthe mandrel, with the threads of the successive layers oriented atvarying angles as discussed hereinabove, the sleevings are placed in amold, the mandrel being used to thread the reinforcing sleevingthereinto. If the centrifugal casting method is practiced, as disclosedby my copending application, Serial 'No. 264,976, filed January 4, 1952,now Patent Number 2,785,442, the mandrel is withdrawn therefrom before apipe is cast with a thermosetting resinous material. If pressure moldingis to be used, as disclosed in my copending application, Serial No.405,339, filed January 21, 1954, now Patent Number 3,037,244, themandrel may be left in place until after the thermosetting resin hasbeen cured, as by heat.

While it is desirable to have the threads of the reinforcing sleeving indirect contact with one another, they can be manufactured to givesatisfactory results with a space between of .001 inch, or they may becrowded toget-her with a negative tolerance of .001 inch. That is, thethreads may be crowded together until the distance between their centersis less than the diameter of the threads in a relaxed position. When socrowded together, it is evident that the threads will be distorted outof round, but this apparently does not decrease the strength of themechanical bond between the fiber and the resin.

It has been determined, however, that there is a direct relation betweenthe size of the mesh opening between the threads and the pressure atwhich a plastic reinforced pipe will leak. As a practical matter, themaximum usable spacing between the threads is .001 inch.

Referring more particularly to FIGURES 11, 12, 13

and 14, in which there are graphical representations of, the relationbetween the numbers of layers of sleeving, and the pounds of pressuralcapacity, expressed in hundreds of pounds per square inch, the curve ofthe theoretical bursting strength is a straight line. In FIGURES 11, 12,and 13 the pressural point at which leakage occurs is indicated by avertical broken line. A comparative examination of these figures clearlyshows the relationship between the size of mesh opening, and the pointat which the fibrously reinforced plastic pipe will fail, throughleakage. As the size of the mesh opening is decreased,the leakagepressure, that is the pressure at which the pipe first gives indicationof leaking, increases materially. As shown in FIGURE 14, when the meshopening is reduced to .001 inch a balanced reinforcement body design isattained. That is to say, the pipe will not leak prior to bursting. Thelast mentioned figure illustrates the results of a test in which areinforced plastic pipe having a mesh opening of .001 of an inch, andhaving the threads wound at a 70 helix angle, reached the 6400 pound persquare inch limit of a testing machine without giving any indication ofleakage. It will be seen that the theoretical burst point of thespecimen used was 6300 pounds per square inch.

It is, therefore, clearly established that as the mesh opening sizedecreased, the pressure that a pipe will stand increases. It would seemthat if the threads are compressed beyond the limit of the negativetolerance given hereinabove, that is, minus .001 inch, the flow of theresinous material will be impeded and there will result dry spots orimproperly wetted areas which may eventually cause a failure of thestructure when it is subjected to high pressures. When a braided sleeveis to be greatly distorted to increase its size or increase its helixangle, it may be necessary to form the element with an increased numberof threads in order to keep the mesh at the desired spacing.

It is evident that this method may be practiced with any of a largenumber of liquid settable materials, including the thermosetting resinsdiscussed hereinabove. It is proposed to use .05 to .125 cobalt as anaccelerator. A peroxide catalyst, such as a product called D.D.M. soldby Wallace and Tiernan, and others, can be used interchangeably withheat, within limits. The catalyst speeds up the curing resin and thecobalt speeds up the catalytic action.

It is also feasible to use particular liquid settable materials toobtain certain physical characteristics in the finished pipe. Forexample, it has been found that a semi-flexible pipe may be formed byusing a 40% flexible resinous material and a rigid resinous material.

It should be clear that it is within the contemplation of this inventionthat pipes or tubular sections may be formed in shapes other thancircular, for example, either elliptical or other shapes which it ispossible to cast. The pipes need not be of uniform cross section, thatis, they may be formed with one or more integral tapers.

Having described only typical preferred forms and applications of myinvention, I do not wish to be limited or restricted to specific detailsherein set forth but wish to reserve to myself any variations ofmodifications that may appear to those skilled in the art and fallingwithin the scope of the following claims.

This is a continuation of my co-pending application Serial No. 459,092filed September 29, 1954, now abandoned.

What is claimed is:

1. A rigid reinforced pipe for sustaining high pressures comprisingthermosetting resinous material selected from a class of polyesterresins, epoxy resins and phenolicepoxy resins and including areinforcement. element of a uniformly interwoven seamless sleevingformed of glass threads, said sleeving being entirely surrounded by amass of said resinous material, the mesh opening in said sleeving beingless than about .001 inch.

2. A rigid reinforced pipe for sustaining high pressures comprisingthermosetting resinous material selected from a class of polyesterresins, epoxy resins and phenolicepoxy resins and including areinforcement element comprising a plurality of layers of uniformlyinterwoven seamless sleeving formed of glass threads, said sleevingbeing entirely surrounded by a mass of said resinous material, the meshopening in said sleeving being less than about .001 inch.

References Cited in the file of this patent UNITED STATES PATENTS1,152,836 Price Sept. 7, 1915 1,520,191 Mackey Dec. 23, 1924 1,978,211Loughead Oct. 23, 1934 2,009,075 Thompson July 23, 1935 2,594,693 SmithApr. 29, 1952 2,594,838 Alexander Apr. 29, 1952 2,690,769 Brown Oct. 5,1954 2,747,616 De Ganahl May 29, 1956 2,807,282 Watts et a1. Sept. 24,1957

1. A RIGID REINFORCED PIPE FOR SUSTANINING HIGH PRESSURES COMPRISINGTHERMOSETTING RESINOUS MATERIAL SELECTED FROM A CLASS OF POLYESTERRESINS, EPOXY RESINS AND PHENOLICEPOXY RESINS AND INCLUDING AREINFORCEMENT ELEMENT OF